[经] marginal production operating cost
biān jì shēng chǎn zuò yè chéng běn ㄅㄧㄢ ㄐㄧˋ ㄕㄥ ㄔㄢˇ ㄗㄨㄛˋ ㄧㄝˋ ㄔㄥˊ ㄅㄣˇ